1. Field of the Invention
This invention pertains generally to hydrocyclones and, more particularly, to the detection of a condition known as roping in the underflow discharge of a hydrocyclone.
2. Description of the Prior Art
When a hydrocyclone employed, for example, in the classification of solids is operating normally, a coarser-solid slurry is discharged through the underflow outlet at the bottom of the separation chamber and a finer-solid slurry is discharged through the overflow outlet at the top. The underflow discharge normally exits from the apex at the bottom of the chamber in the form of a conical spray with an included angle greater than about 20 degrees. A splash skirt is used below the apex of the hydrocyclone to contain and direct the flow downward and to reduce splashing and misting.
As defined in the art, roping occurs when the amount of solids reporting to the underflow outlet increases to the point where the discharge rate through the apex limits the flow. As a result, the coarse solids begin to build up in the separation chamber and pass through the overflow, the internal air core in the separation chamber collapses, and the underflow discharge becomes a tight cylinder or rope of coarse material. If this roping condition is not corrected, the underflow can plug off completely, and the cyclone will pass the entire flow through the overflow.
Normal discharge and roping are illustrated in FIGS. 1A and 1B, respectively.
In closed-circuit grinding applications, the cyclone underflow density is preferably kept high so that a minimum amount of water accompanies the coarse solids. That is done by sizing the apex, or orifice, to limit the flow to the solids plus no more than about 50% water. If the apex is too large, more water will report to the underflow with a large quantity of fine solids entrained in it. If sent back to the mill, those fine solids will limit classification efficiency as well as new feed capacity.
Most plants have a number of operating and standby cyclones which are brought into and out of operation with automated valves operated from a control room. With variable tonnages and ore hardness, it is difficult to operate the cyclones with maximum underflow density and at the same time avoid roping and the problems associated with it.
Heretofore, there have been some attempts to avoid the problem of roping by monitoring the angle of the underflow discharge stream to determine whether it is within predetermined limits. Examples of this approach are found in U.S. Pat. No. 3,114,510 and No. 4,246,576. In addition, U.S. Pat. No. 5,248,442 discloses a system in which information about the underflow shape is combined with data about the flow rate and density of the feed stream to provide information about the feed stream, the underflow stream or the overflow stream.